Conventional ECUs for vehicles, to secure high reliability thereof, are installed with a process designed to monitor execution of a program of a microcomputer installed therein and to reboot the microcomputer to prompt it in case the program execution is interrupted or hung for some reasons.
As an example of such a process, a custom watchdog IC (Integrated Circuit) is provided to be electrically connected to a microcomputer; this watchdog IC has the monitor and reboot functions. Specifically, the watchdog IC is designed to monitor execution of a program of the microcomputer and to reboot the microcomputer based on the monitored result. An example of the structure with the watchdog IC, which can realize such a malfunction monitoring process, is typically disclosed in Japanese Unexamined Patent Publication No. H07-114490 (see FIG. 29).
As illustrated in FIG. 29, with the structure disclosed in the Publication No. H07-114490, in order to substantiate the malfunction monitoring process, a watchdog IC 102 is configured to be electrically connected to a microcomputer 101 as a target to be monitored.
In the malfunction monitoring process, the microcomputer is configured such that an interrupt occurs every predetermined period during execution of a program, such as an initialization program. If it is determined that a task with low priority is not executed by the microcomputer during execution of the program even though the number of interrupts reaches a predetermined number, the watchdog IC is configured to reset the microcomputer.
With the malfunction monitoring process disclosed in the Publication No. H07-114490, the order of the priority of all tasks included in the program need to be managed to change the algorithm of the program or the specs on the microcomputer. This may cause deterioration of the maintainability of the program to be inevitable.